So I need some advice here. Not really sure what to do. I am shooting video of a ship wreck next week (The Duane in Key Largo). Most of the shooting will take place at around 100ft. Here is my underwater video setup:

Now for my question. If you take a look at the red filter that I am using, in the description on B&H it states that it will work in "up to 70ft of water." So what happens to your colors after you pass 70ft? I am not using a light, so I am wondering if I should just shoot the Duane without this red filter and without a light. I mean, what are my options? And what is the smartest way to go?

I've been shooting on the shallow reefs of Key Largo, and I must say the red filter (with no lights) does do the job well, giving me nice color. I just don't have any experience shooting in the depths below 70ft. And I really want to know why this filter says it's only good for 70ft...

The red filter replaces lost red, the first colour to be lost in the colour spectrum. After 70 ft other colours are also lost and you would only be replacing red with your filter but not the other lost colours...

well.. the red filter also means you are losing a stop or two of light, at 100 feet you could use that extra light. Video lights are only good for stuff up to about 6 feet away, so they are good to light up close up shots of the wreck but they won't help if you are trying to get general "scenic" shots. I don't know the wreck so not sure if it has king posts and such that come shallow? Your filter would still be good for those, however, filter is really only effective until 50 feet, not 70 in my experience. Does the filter have a flip? or will it be fixed to the lens? If its a flip then you can try both and see what works better. Perhaps you can borrow or rent some lights for the closer shots?

No it doesn't have a flip. What exactly IS a flip? Mine is just a thread mounted filter, fixed to the lens. Again, here is the one I am using.

Yeah I plan on just getting wide establishing shots, and I will most likely steer clear of any close ups. Stinks because I've heard that the Duane is covered in beautiful, colorful coral. But just curious, what will it look like if I get super close with just a red filter and no lights? I know that without the red filter and no lights that it will be cyan. So what is cyan plus a little red? hmm I don't know...

I guess I could look into light rentals, if they are in my price range.

We used very successful a red filter on a professional Canon HD video camera between 25 and 35 meters on our "housewreck" in
the clear waters of Sardinia with the best results around noon when the sun is high and strong.
The video has clearly much more contrast and clarity and the colors are a bit more visible, but still not enough color to be "colorful".
Anyway even with the strongest video lights you will have problems to illuminate a big wreck and i personally like the blueish - and natural -hue of
ambient lights shots or recordings.

Yeah I understand that you can't really light for a wide shot of a huge wreck, but I was just worried that having the red filter on there might make it worse. Looks like I am going to keep the red on there and shoot away. If I remember I will post some screen grabs or maybe even a clip.

a flip is a mount that the red filter fits into and sits between the lens and the port. You can flip it down in front of the lens when you want to use it and flip it up out of the way when you don't.. its very handy.. not sure if Ikelite has that option but you may want to ask them

'Deep' video will require some creative lighting, both on-camera and off-camera. Presently, I'm working on a project which will mount 21,000 lumens on-camera / on-me, not to mention the lighting off-camera/me. Of course, having that degree of lighting is not license to use it...

There is nothing magical about the 70ft. For every 2-3m of water your reds loose a stop or so more than the blue/greens and the white balance needs to boost reds to compensate. This works until the boosted red becomes too noise. You can also boost the reds by increasing the exposure and you can do so without blowing out the blue/green by a red filter that selectively filters out blue/green. Depending on how strong the filter is you gain one or two stops of red, which means you can go something like 3-6m deeper than if you had not used the filter. If you go very deep the filter still helps but it would need to be much stronger to properly re-balance the red with blue/green. You can stack filters but loosing to much green/blue makes proper exposure and focusing more difficult.
One thing to remember is that the red channel of the sensor represents a broad wavelength range. The longest wavelength reds will disappear fastest and filters don't really help much with those, whereas the shorter wavelength reds will fare better and may still be present on your deeper dives.

I'd say do some dives with filter for the wide and accept that you will get noise past a certain depth, then do another with the lights for closer shots to mix things up and get some colour of those corals coming through, povs even interiors if that's your cup of tea.
That's the big problem when you don't have a flip, can't swap mid dive when you have the opportunity, unless you can re- white balance the cam with the filter and lights to compensate for the filter.
Dive safe

Wow thanks for all of the great info guys. Looks like I will go with the filter and start saving for some lights!

I am diving the Duane (100ft) this Monday, so I will for sure post some screen grabs from the video so you can take a look. I am also diving the Benwood, which is a WWII wreck sitting in about 25ft - 45ft of water, and I am sure the red filter will rock and roll on that dive. I am really excited!

The red filter replaces lost red, the first colour to be lost in the colour spectrum. After 70 ft other colours are also lost and you would only be replacing red with your filter but not the other lost colours...

Don't want to be picky but one of the common misconceptions about the red filter is that it "replaces lost red". It can not. Red light that has been absorbed by the water is gone. Can not be replaced by a filter (only a artificial light can do that - and only over very short distances). The red filter looks red because it does not allow blue and green to pass through it.

Why is this important?

Because, if you don't understand what is really happening with the light and colours, you'll make wrong choices.

The red filter is reducing blue and green.

If there is enough red left in the ambient light, it will reduce blue and green, shifting the balance between the three primary RGB colours, creating the appearance of more red. If there is none or little red left, it wont help at all.

But, by reducing blue and green, it is reducing the total amount of light that the sensor is receiving. So, if the sensor is struggling to get enough light to get a decent image, you are just making it worse. Different cameras react differently. Some try to boost the light by amplifying it (gain). This can cause ugly fuzzies.

So a red filter (should really be called a "blue and green reduction filter") is only useful if there is a lot of ambient light and some red left in the mix of ambient light.

The depth range in which it is actually useful varies a lot from dive to dive and even during the dive as the sun disappears behind clouds. As a rule of thumb, you'll get some improvement between 5 to 15 meters with a red filter. If it very sunny, don't swing it in until 8 meters deep, otherwise some things will look too red. If it is cloudy start using it from 5 meters deep. Definitely have it swung out by 15 to 18 meters deep as you are just losing light to the sensor. There is no R left to "balance" with the GB.

If you turn on video lights, flip out the red filter. if you do a silhouette by pointing the camera towards the sun, flip out the red filter.

Better than a red filter, if you have a camera that can do white balance in low light, I suggest that you forget about the red filter all together and just set a suitable white balance for the depth that you are at. But that's a whole new story...

I personally wouldn't use the red filter. The dslrs are good in low light, and as long as you get a good white balance, you should have good footage. I personally don't like a red filter, below 40. So I typically end up never putting it on. You may need to up your ISo a bit. In your particular instance, I would think light is going to be more importannt than color. If you do a red filter, you are going to lose 2 stops of light. Thus pushing your ISo too high and being too noisy.

white balance is the sure way to go. If you don't want to do it once you reach the wreck, find some picture of a wide shot of a 100 ft deep wreck on the web that hasn't been color corrected and do a white balance on a section of the picture that should be white but is very bluish. If the camera has multiple white balance memory, do some WB for variation of bluish water like deep blue, shallow blue, etc. Then depending on your depth, just recall the one that looks apropriate.

Take a picture of a white object – fill the entire frame with white
Menu: 4th tab says ‘custom WB’
Choose the white picture
Click on Set
Go to movie mode
Click the quick menu button and cursor over to WB and change it to the custom setting

Instead of a white object, you might use something that has some red in it so that the camera does not to push the white balance beyond a reasonable balance. Rust, brown coral, human skin, pink fins all enough red in them to help get a better UW WB.

Interesting thread but filters can actually be useful
If we are talking stills in post processing you can do what you like in video you need to be the footage to be nearly there already
Cameras when setting custom white balance usually range between a max value of 8000-9900 and allow limited changed to tint
In some days color temperature underwater is above 10,000 plus stretching the camera white balance to boundaries creates noise in those circumstances the warmth of the filter helps taking down temperature a few 1,000K that helps let alone the tint adjustment
It is trued that in low light conditions filter as they take 1-1.5 stops end up with the camera increasing gain and creating noise to a point that can be unbearable but is not true that a filter absorbs more as you go deeper, the light goes missing by itself that is what looses exposure
So as you go down the combination of less light and the added 1.5 stops of the filter make your camera behave so badly that is not worth having a filter
What depth is workable depends on camera performance at high gain, general brightness and light conditions, visibility etc the manufacturer specs are a broad recommendation